1. Technical Field of the Invention
The invention relates generally to line drivers for communication networks; and, more particularly, it relates to multi-mode line drivers for communication networks such as xDSL networks.
2. Description of Related Art
Line driver circuits are typically used to amplify the strength of input signals (digital or analog) and drive the signals over a transmission line. In certain applications, such as processing discrete multitone (DMT) signals in high data rate modem-related applications that must support wide signal swings on a line, line driver circuitry must adhere to relatively strict operating parameters, and may consume a relatively high percentage of system power.
For example, DSL (digital subscriber line) technology provides for the digital transmission of data over the wires of a local telephone network. Typically, in a DSL-based communication system, an Internet service provider (ISP) interfaces with an analog telephone line using a DSL modem. The DSL modem enables the ISP to communicate with consumers over the analog telephone line. Likewise, a consumer interfaces with the analog telephone line using a DSL modem to perform communications with the ISP. The DSL modem of the consumer extracts digital data from the analog telephone line that was transmitted by the ISP, and may provide the extracted digital data to a consumer device or network. Furthermore, the DSL modem of the consumer transmits digital data to the ISP over the analog telephone line. Typically, the download speed of consumer DSL services ranges from 512 kilobits per second (kbit/sec) to 24,000 kbit/sec or greater, depending on the type of DSL technology.
Various types of DSL technology exist, including Asymmetric Digital Subscriber Line (ADSL) and VHDSL or VDSL (Very High Speed DSL). In ADSL, upstream communication speeds (e.g., for transmissions from the consumer) are lower than downstream communication speeds (e.g., for transmissions from the ISP). With standard ADSL, a frequency band of 25.875 kHz to 138 kHz is used for upstream communications, and a frequency band of 138 kHz-2.2 MHz is used for downstream communications.
VDSL is a newer standard that provides for faster data transmissions than standard DSL or ADSL. For example, VDSL is capable of supporting high bandwidth applications such as HDTV. Communications according to VDSL are symmetric such that upstream and downstream communications may be performed at the same rates. Second-generation VDSL (VDSL2) systems utilize a bandwidth of up to 30 MHz to provide data rates exceeding 100 Mbit/s in both the upstream and downstream directions. The maximum available bit rate may be achieved at relatively short ranges, such as a range of up to about 300 meters.
As the different types of DSL technologies become more widespread, DSL modems capable of supporting multiple DSL standards (such as ADSL and VDSL2) are desired. However, to save costs, it is desired for DSL system solutions to use fewer components to reduce the resulting bill of materials (BOM). Such cost pressures, coupled with line driver power consumption requirements and other considerations, make it challenging to implement sufficiently acceptable DSL modems with multi-DSL technology capabilities.